1. Field of the Invention
The present invention relates to a method for detecting system faults in an on-board central tire inflation system of the type having a plurality of inflatable tires each fluidly communicatable individually or as a group or groups by branch conduit means to a common central conduit which may be otherwise fluidly isolated or connectable to a source of pressurized fluid or to an exhaust to atmosphere and having pressure measurement means for measuring a pressure value indicative of the inflation pressurization of the central conduit. Preferably, each of the tires will have a wheel-end valve for selectively establishing or blocking fluid communication between the tire and the common central conduit.
2. Description of the Prior Art
Central tire inflation systems ("CTIS"), also known as tire traction systems, are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 2,634,782; 2,976,906; 2,989,999; 3,099,309; 3,102,573; 3,276,502; 3,276,503; 4,313,483; 4,418,737; 4,421,151; 4,434,833; 4,640,331 and 4,678,017, the disclosures of all of which are hereby incorporated by reference. CTIS allow the operator to remotely manually and/or automatically vary and/or maintain the inflation pressure of one or more of the vehicle tires from the vehicle (usually a truck) air system, usually while the vehicle is in motion as well as when the vehicle is at rest.
It is well known that the traction of vehicles on relatively soft terrain (i.e. on mud, sand or snow) may be greatly improved by decreasing the inflation pressure within the tires. By decreasing the inflation pressure, the tire supporting surface (usually called the "footprint") will increase thereby enlarging the contact area between the tires and the terrain. Additionally, it is often desirable to decrease the tire pressure from the over-the-road or highway inflation pressure to increase riding comfort on rough roads. On the other hand, higher tire pressures decrease rolling resistance and tire carcass temperatures on smooth roads thereby increasing economy and safety. Accordingly, in cross country vehicles it is desirable to change the inflation pressure in the pneumatic tires to fit the terrain and is also desirable that a system be provided for changing the inflation pressure of the tires from an on-board source, while the vehicle is at motion or at rest and that the system be controlled from the vehicle's operating cab.
In a particular type of CTIS, as illustrated and described in above-mentioned U.S. Pat. No. 4,640,331, a plurality of wheel ends (each comprising one or more tires) are each, individually or as a group or groups, fluidly connectable by a separate branch conduit to common central conduit which may be connected to a source of pressurized air for inflating the tires, to a source of regulated pressurized air for deflating the tires and/or, to atmosphere for venting the conduits and relieving pressure across the rotating seals. The common conduit may also be pressurized by means of a quick release valve or the like to the average pressure of selected ones of the various branch conduits. A single pressure transducer is provided in fluid communication with the common central a value indicative of the pressure or average passage in selected ones or groups of the inflatable tires.
The CTIS source of pressurized fluid is, preferably, the on-board air system comprising a brake wet tank supplied by an engine driven compressor. The wet tank is provided with a two-position pressure switch which will automatically open to block fluid communication between the wet tank and CTIS if wet tank pressure falls below a minimal pressure (i.e. almost 80 psia) required for safe brake system operation and will automatically close when the tank pressure achieves a safe value (i.e. about 115 psia) for diverting pressurized air from the brake system to the CTIS. The switch is preferably provided with means to provide output signals indicative of the open or closed condition of the wet tank pressure switch.
While the on-board CTIS described above is highly advantageous as pressure venting is remote from the wheel ends, the conduits and seals are vented to atmosphere during system inactive (steady state) conditions and a single pressure transducer, located in a relatively well protected location remote from the wheel ends and/or the vehicle under carriage, can be utilized to sense tire inflation of the vehicle tires or groups of tires, the CTIS was not totally satisfactory as methods for detecting, on a self-diagnostic basis, conditions indicative of certain system faults and/or vehicle conditions requiring CTIS shutdown, were not provided.